The present invention relates to seals and in particular to seals interposed between the platforms of blades in a rotor.
A conventional fan rotor for compressing air comprises a disc having a plurality of radially extending blades mounted thereon. The fan blades are mounted on the disc by inserting the radially inner end of the blades in correspondingly shaped retention grooves in the radially outer face of the disc. The fan blades do not have platforms so separate wall members bridge the space between pairs of adjacent blades to define the inner annulus wall for the compressed air. Each wall member is separated from the adjacent blades by a small gap, which accommodate manufacturing tolerances and changes to the blade shape during operation of rotor.
A void exists between the wall members and the radially outer face of the disc. This void is full of air, which is at a higher static pressure than the air in the blade passages. Seals are therefore used to bridge the gap between the wall members and the blades to prevent air flow from the void into the blade passage.
It is known to use seals made from resilient materials, which are bonded to the edges of the wall members adjacent the blades to seal the gap therebetween. The seals are designed to be urged radially outward into engagement with the blades as the rotor rotates.
One such seal is disclosed in EP-0640172 which is owned by the applicant. In the arrangement described the resilient seal strip has an undulating flange portion which is inclined radially inward. In operation the flange portion is deflected radially outwards by centrifugal forces as the rotor rotates and engages with the adjacent fan blades to seal between the wall members and the adjacent blades. The undulations are substantially sinusoidal and enhance the flexibility of the seal member. The undulations however create smaller voids in which air re-circulates to disrupt the airflow in the blade passage.
The present invention seeks to provide an improved seal in which seal voids are minimised to avoid re-circulation and so improve the aerodynamic performance of the seal.
According to the present invention there is provided a seal for reducing the gap between adjacent members which are arranged circumferentially in a rotor, the seal has a flange portion which is inclined radially inwards, a cavity is located in the flange portion of the seal whereby in operation the flange position is deflected radially outwards and the cavity fills with a fluid to inflate the seal.
Preferably the cavity has at least one opening which is in communication with a fluid which in operation passes through the rotor. The fluid which passes into the cavity to inflate the seal is preferably air.
In the preferred embodiments of the present invention the seal consists of a bellows which define the cavity. The bellows may be formed from a resilient material such as rubber.
Preferably the rubber is reinforced. The rubber may be reinforced by at least one carbon composite member. The carbon composite may be either a single strip having slots therein, to render it sufficiently flexible to accommodate the curvature of the adjacent blades, or a plurality of discrete carbon composite panels.
In addition to the carbon composite the seal may be further reinforced with a fabric such as polyester. The fabric reinforcement may extend around the carbon composite member.